A Comparison of the Fixation Strengths Provided by Different Intraosseous Tendon Lengths during Anterior Cruciate Ligament Reconstruction: A Biomechanical Study in a Porcine Tibial Model

BACKGROUND: The purpose of this study was to determine the tibial fixation strength provided by different intraosseous soft tissue graft lengths within the tibial tunnel. METHODS: Porcine tibial bones and digital flexor tendons were used for testing. Bone mineral densities of proximal tibial medial condyles were measured, and two-strand tendon bundles of 8 mm diameter were used. An intraosseous graft length of 2 cm was used in group 1 (n = 10), and a graft length of 4 cm was used in group 2 (n = 10). Tunnels were 4 cm in length and 8 mm in diameter. Tibial fixation was performed using a suture tied around a screw post with a washer and an additionally inserted 7 x 20 mm bioabsorbable screw. After applying preconditioning loading of 10 cycles, 1,000 cycles between 70-220 N were applied at a frequency of 1 Hz. Graft slippage and total graft movement were recorded. Ultimate tensile strength was measured by pull-out testing at an Instron crosshead speed of 1,000 mm/min. RESULTS: No significant intergroup difference was found for total graft movement after cyclic loading (slippage in group 1, 1.2 mm and group 2, 1.2 mm, respectively, p = 0.917; and total graft movement in group 1, 3.3 mm and group 2, 2.7 mm, respectively, p = 0.199). However, mean ultimate tensile strength in group 2 was significantly higher than that in group 1 (group 1, 649.9 N; group 2, 938 N; p = 0.008). CONCLUSIONS: In a porcine model, ultimate tensile strength was greater for a 4 cm long intraosseous flexor tendon in the tibial tunnel. However, no intergroup difference in graft slippage or total graft movement was observed. The results show that a 2 cm intraosseous graft length in the tibial tunnel is safe and has sufficient strength (> 450 N) for adequate rehabilitation after anterior cruciate ligament reconstruction.

A Clinical Result of Pedicle Screw Fixation in Osteoporotic Spine: Complications and Prevention

STUDY DESIGN: Retrospective study. OBJECTIVES: To analyze the clinical results of patients who were treated by pedicle screw fixation in osteoporotic spine and suggest the methods for preventing a loss of fixation strength. SUMMARY OF THE LITERATURE REVIEW: There are some methods to decrease failure rate and increase fixation strength in the osteoporotic spine: use bicortical screw, cement augmentation and supporting anterior column by interbody fusion using cages. MATERIALS AND METHODS: Forty-four patients treated by spinal instrumentation using pedicle screw from 2004 to 2011 were followed for at least 12 months. Five men and 39 women were diagnosed as osteoporotic spine (T score <-3.0). Two hundred forty eight pedicle screws were included and statistically analyzed the correlation between the use of bicortical screw, cement augmentation, anterior column support and fixation loss of the pedicle screw. Radiologic results were evaluated to find out the mechanical complications, like loosening of the screw, fixation failure, and nonunion. RESULTS: There were 9 complications associated with mechanical strength, loosening of pedicle screws in 7, sinking down of cage in 4, and nonunion in 4 cases. Using bicortical pedicle screw, cement augmentation and anterior column support were significantly correlated with the increasing fixation strength (P=0.001, P=0.047, P=0.014). In addition, these three factors contribute to stabilize the instrumentation (Linear by linear association, P=0.012). CONCLUSIONS: These 3 methods, using bicortical pedicle screw, cement augmentation and supporting anterior column, are effective to enhance the fixation strength and prevent loss of holding power in the osteoporotic spine.

Comparison of fixation strength of the locking and non-locking anterior cervical plate systems / 第二军医大学学报

Objective: To compare the prompt fixation strength and antifatigue strength of the locking and non-locking anterior cervical plating systems. Methods:AO Cervical Spine Locking Plate (CSLP), Danek Orion plate and AcroMed Acroplate were used on the lamb cervical spines. The CSLP and Orion were tested with screws locked and unlocked, and the Acroplate with unicortical and bicortical purchase. The fixation strength and pull-off strength of the screw-plate constructs were performed initially and after fatigue. Results: Locked CSLP and Orion constructs were more rigid than all unlocked unicortical systems initially and after cyclic loading. After fatigue testing, the strength of all unlocked constructs decreased significantly. There was no significant difference in pull-off strength between the CSLP, the Orion and the unicortical Acroplate. Conclusion: The locking mechanism significantly increases the prompt fixation strength and antifatigue strength of the tested screw-plate systems.

Comparison of fixation strength of the locking and non-locking anterior cervical plate systems / 第二军医大学学报

Objective: To compare the prompt fixation strength and antifatigue strength of the locking and non-locking anterior cervical plating systems. Methods:AO Cervical Spine Locking Plate (CSLP), Danek Orion plate and AcroMed Acroplate were used on the lamb cervical spines. The CSLP and Orion were tested with screws locked and unlocked, and the Acroplate with unicortical and bicortical purchase. The fixation strength and pull-off strength of the screw-plate constructs were performed initially and after fatigue. Results: Locked CSLP and Orion constructs were more rigid than all unlocked unicortical systems initially and after cyclic loading. After fatigue testing, the strength of all unlocked constructs decreased significantly. There was no significant difference in pull-off strength between the CSLP, the Orion and the unicortical Acroplate. Conclusion: The locking mechanism significantly increases the prompt fixation strength and antifatigue strength of the tested screw-plate systems.

Comparison of fixation strength of the locking and non-locking anterior cervical plate systems / 第二军医大学学报

Objective: To compare the prompt fixation strength and antifatigue strength of the locking and non-locking anterior cervical plating systems. Methods:AO Cervical Spine Locking Plate (CSLP), Danek Orion plate and AcroMed Acroplate were used on the lamb cervical spines. The CSLP and Orion were tested with screws locked and unlocked, and the Acroplate with unicortical and bicortical purchase. The fixation strength and pull-off strength of the screw-plate constructs were performed initially and after fatigue. Results: Locked CSLP and Orion constructs were more rigid than all unlocked unicortical systems initially and after cyclic loading. After fatigue testing, the strength of all unlocked constructs decreased significantly. There was no significant difference in pull-off strength between the CSLP, the Orion and the unicortical Acroplate. Conclusion: The locking mechanism significantly increases the prompt fixation strength and antifatigue strength of the tested screw-plate systems.

A Biomechanical Study of Screw Designs of Transpedicular Screw on the Fixation Strength / 대한정형외과학회잡지

INTRODUCTION: The fixation strength of transpedicular screw system in the vertebral hody relied on bone quality and anatomical characteristics of vertebral pedicle, designs of screw and types of connection(rod or plate) with screw. The purpose of this study is to verify the biomechanical nature of the transpedicular fixation in spine under various conditions with porcine vertebrae. MATERIAL AND METHOD: Fresh porcine vertebrae and the custom-made screws were used in this experiment. To reduce the errors caused by vertebral bodies of different size and quality, vertebral bodies having regular range of pedicular width(10.0 to 11.5mm) and hone density(more than 1.0 gm/cm2) were used. The pedicle screws were inserted in the same procedure and axial pull out test was performed with using the Material Testing System(lntron8511, Canton, USA). The experiments were performed in four types to assess the difference of strength accroding to designs of the screw hy using two group of screws. The first group of screw was designed according to the outer and inner diameter and the second group was designed according to the shape, pitch, and thread profile of screw. Experiment I was perfomed to evaluate the effect of screw diameters on the biomechanical pull-out strength hy using the first group of custom-made pedicle screw which fixed all other factors except the diameter of screw. Experiment I was to verify the effect of screw shape, experiment III to verify the effect of pitch and experiment IV to verify the effect of thread profile. RESULTS: The results of experiments were summarized as follows: Experiment I showed that the screw of larger outer diameter had greater holding strength. Experiment II showed that the holding strength of cylindrical shaped screw is superior to that of conical shaped screw. Experiment III showed that there is no statistical significance between different modes of pitch. Experiment IV showed that the holding strength of buttress shape of thread profile is superior to that of V-shape. CONCLUSION: It seemed that the fixation strength of the screw was more powerful with 1 mm increment of outer diameter in 4-7mm of outer diameter, 3mm of pitch and buttress shape of thread of the screw with the same operation technique.

Biomechanical Study of the Pull-Out Strength of Interference Screw Fixation in Anterior Cruciate Ligament Reconstruction: Comparison Between Endoscopic and Arthroscopic Assisted Technique / 대한정형외과학회잡지

Surgical reconstruction of the anterior cruciate ligament is undergoing constant evolution. The variable success of these procedures can be attributed to many factors including graft selection, graft placement, graft tensioning, graft remodelling and rehabilitation program. Rigid fixation is probably the most important factor in the success of these procedures during the initial stages of healing. Arthroscopically assisted reconstruction of the ACL-deficient knee using a bone-patellar tendon-bone graft(two-incision technique) is a reliable and evolving technique. Rosenberg et al, described a one-incision technique that allows endosteal fixation of bone plugs within their femoral tunnels intraarticularly via the intercondylar notch. These two techniques are different from their femoral tunnel direction and bone plug placement. The present study was designed to develop a swine model for in vitro biomechanical testing of the bone-patellar tendon-bone ACL autograft to compare the pull-out strength of Outside-In technique and Inside-Out technique. The result were as follows: 1. Normal ACL(N=10 knees) pull-out tensile strength tests showed a maximum tensile strength of 1295.34(N), a stiffness of 120.95(N/mm), and a linear load of 1104.26(N). The failure sites were all tibial attachments. 2. Femoral and Tibial interference fit pull-out tensile strength tests(N=10 knees) showed a maximum tensile strength of 463.23±42.27(N), a stiffness of 33.62±3.18(N/mm), and a linear load of 392.51±95.42(N). The failure sites were all in the tibial tunnel area(N=9 knees), except for one which femoral tunnel area. 3. Inside-Out technique(N=15 knees) showed a maximum tensile strength of 1250.64±75.67(N), a stiffness of 94.31±26.44(N/mm), and a linear load of 1046.92±367.55(N), but the Outside-In tech-nique(N=15 knees) showed a maximum tensile strength of 805.35±54.61(N), a stiffness of 83.33±10.98(N/mm), and a linear load of 685.99±86.32(N)(p < 0.0001). The failure sites were all in the femoral tunnel area. 4. Tensile testing demonstrated that the Inside-Out technique was significantlly stronger than Outside-In technique for maximum tensile strength, stiffness and a linear load.

A Biomechanical Study on the Fixational Strength of the Trans-pedicular Screw: In vitro measurement / 대한정형외과학회잡지

With porcine vertebrae, the static and dynamic holding power of the pedicle screws under various conditions were measured to understand the biomechanical nature of the transpedicular screw fixation in spine. The objectives of the present study were; (1) to find the correlation between the insertion depth of the screw and the resulting holding power, (2) to determine the effect of bone cement augmentation on the screw fixation in a loosened hole, and (3) to assess the load-sharing mechanism between the cortical and the cancellous one surrounding the screw in this fixational system. The geomorphological characteristics of each porcine vertebra was measured directly with a micro-caliper. The bone mineral density of the specimens was also measured. Material with screw was holded in the fixed cross head of material testing system(Autograph E-10T). Testing force was applied and graph was obtained in the chart record. The results of the static pull-out tests in this study showed that there was a statistically-significant positive correlation between the screw diameter and the pull-out resistance(p < 0.05). The strength of the fixation did not actually increase as much as the insertion depth of the screw increased in these tests(r=0.457). In low-cycle fatigue tests, the increased number of cycles was required to clinical failure in the deeper-inserted crews. Considering the mechanical failure, a statistically-significant positive correlation between the failure cycle and the insertion depth was observed in both deep and shallow insertion groups(p < 0.05). Nonpressurized PMMA augmentation appeared to restore the ability of the screws to withstand pullout loading of the original value. On the effect of the cortical and cancellous bone, the most important factor was the cortical bone of the entrance near the screw.